1. Field
The present invention relates generally to an alignment key of a semiconductor device and a method of fabricating the same, and more particularly, to an alignment key of a semiconductor device capable of detecting a stable alignment signal and a method of fabricating the same.
2. Discussion of Related Art
In manufacturing a semiconductor device, various conductive patterns including contact holes are created by forming a predetermined thin layer on a wafer and progressing a lithography process to establish a desired circuit pattern.
The lithography process includes applying a photoresist layer on a to-be-etched layer, exposing the photoresist layer by using a photomask, and developing the exposed photoresist. Various conductive patterns including contact holes are formed by etching the to-be-etched layer by using the formed photoresist pattern.
It is necessary to accurately align the wafer and the photomask in order to perform the lithography process, since there is demand for semiconductor devices with a multi-layered structure with high accuracy of overlay between upper and lower layers.
Accordingly, in a conventional process of manufacturing a semiconductor device, an alignment key is inserted in order to recognize the accuracy of overlay between upper and lower layers.
The alignment key, which is a kind of pattern formed on a wafer for aligning a photomask called a reticle at an accurate position, is formed on a scribe region of a wafer that does not exert influence on a cell region, and a process of forming the alignment key is simultaneously performed with a process of forming an actual pattern on the cell region before the lithography process.
However, in the implementation of the three-dimensional device, due to an increase in the number of stacks, a laser beam incident as an alignment signal and a laser beam reflected from a semiconductor substrate 10 are offset, thereby weakening a measured signal. Accordingly, an error of alignment accuracy may be generated.